Modification of a microbial co-polyester by graft copolymerisation

Wormald, PS 1998, Modification of a microbial co-polyester by graft copolymerisation , PhD thesis, University of Salford.

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The principal objective of this project was to introduce specific properties in to a polymer required by the sponsor company, Bonded Fibre Fabric, namely appropriate thermal characteristics coupled with biodegradability. Microbial polyesters are biodegradable, but no commercial grade was available that met the required thermal criteria detailed below. Therefore it was decided to attempt to lower the thermal softening temperature by grafting chains of poly(methyl acrylate), (which softened at the required temperature) to the microbial polyester backbone selected for this work was poly(3-hydroxybutyrate-co-3- hydroxyvalerate)(,P HV). PHV is very stable chemically and of the three methods attempted, that employing gamma irradiation to produce polymer peroxides gave the highest grafting add-on. Fundamental work was carried out on the interaction of gamma rays with the polymer substrate. These interactions were monitored via esr spectroscopy. A G(radical) value for the polymer was determined as 1.7 (heV)'1 by comparison to an irradiated standard, (glycine). Initial reaction conditions for mutual irradiation graft copolymerisation were established by swelling followed by subsequent extraction of monomer from the film and quantitative analysis. The inevitable production of homopolymer during irradiation was suppressed by the inclusion of cupric chloride. Graft copolymerisation was effected via mutual irradiation and monitored by gravimetric and nmr analysis. A maximum grafting add-on of 17wt% was obtained. A second graft copolymerisation technique involving irradiation, namely preirradiation peroxide grafting was also attempted. The formation and stability of the radicals produced on irradiation of the polymer in vacuo were confirmed by esr, as was radical decay on exposure to air. Peroxide groups were also qualitatively determined chemically. Both techniques gave a strong indication that peroxide groups were formed on irradiation in air. In grafting experiments the peroxidised PHV was found to produce grafting add-on, which was again confirmed by gravimetry and nmr. The extent of grafting was much greater via this technique when compared to mutual irradiation. Grafting add-on figures in excess of 200wt% were obtained with minimal production of homopolymer. The level of grafting was shown to depend on the monomer concentration in the medium, the preirradiation dose, reaction time and temperature. Thermal analysis showed that grafting occurred in both the crystalline and amorphous regions for higher grafting add-on, but only in the amorphous region for lower add-on. It was also demonstrated that this technique could be applied to other acrylic monomers, namely n-butyl acrylate, ethyl acrylate and also to methyl methacrylate. Grafting was once again confirmed by gravimetric and nmr analysis. Biodegradation results were disappointing on grafted materials when compared to those on an ungrafted sample. It appeared that the grafted chains were interfering with biological activity. It was thought that the hydrophobicity of the grafted chains inhibited the take up of water essential for microbial growth. In addition to graft copolymerisation employing gamma irradiation techniques, the route exploiting chain transfer reactions was also explored. However, although graft copolymers were obtained, they were accompanied by the inevitable production of homopolymer. Finally, a short section is included that details overall conclusions and suggestions for further work.

Item Type: Thesis (PhD)
Depositing User: USIR Admin
Date Deposited: 13 Jul 2017 15:16
Last Modified: 27 Aug 2021 20:41

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